What was the distance of the pitchers mound to home plate before it was 60ft 6in?

When the National League started in 1876 the back line of the pitcher's box, which was on flat ground, was 50 1/2 feet from home plate and the box's dimensions were 6 feet by 6 feet. The pitcher could start his delivery with his back foot anywhere touching the back line. The distance between home plate and the back line of the box was changed in 1881 to 55 1/2 feet. In 1886, the box's dimensions were changed to 4 feet by 7 feet. Offense went up and the next year the box's dimensions were changed to 4 feet by 5 1/2 feet where it stayed until 1893 when the pitching mound was introduced and a rubber slab, 12 inches in length, was used for the pitcher to put his back foot. This was done for offense and the NL's batting average went up 35 points in 1893 and another 29 points in 1894. Because of the increase in offense, the pitching rubber was lengthened to 24 inches in 1895.